The olefin metathesis reaction has established itself as one of the most powerful chemical reactions available for the synthetic preparation of alkenes. In recent years, a great deal of research has been directed to the development of new catalyst systems for use in olefin metathesis, with catalysts that incorporate transition metals such as ruthenium, molybdenum, or tungsten receiving the lion's share of attention within the chemical community. Two perennially popular catalysts systems are the ruthenium catalysts developed by Nobel laureate Robert H. Grubbs and the molybdenum and tungsten catalysts developed by Nobel laureate Richard R. Schrock.
One criterion by which to judge the efficacy of a metathesis catalyst is the turnover number (“TON”) that can be achieved prior to deactivation of the catalyst. Often, catalyst systems that show efficacies in catalyzing an olefin metathesis reaction are susceptible to a variety of contaminants that may significantly reduce the TON that otherwise can be attained.
Natural feedstocks including but not limited to natural oils (e.g., vegetable oils, algal oils, animal fats, tall oils, and the like) and derivatives of natural oils (e.g., fatty acids and fatty acid esters) can be converted into industrially useful chemicals through olefin metathesis. However, catalyst efficiency and product conversion can vary dramatically depending on the purity of the feedstock that is being metathesized. One challenge in using natural feedstocks is that they may include impurities—sometimes in trace amounts—that do not exist in petroleum feedstocks. Often, these impurities react (and/or otherwise interact) with the metathesis catalyst and may drastically affect the efficiency of the catalyst and metathesis reaction. Moreover, the presence and level of various impurities in natural oils may vary from batch-to-batch, depending, for example, on the geographic location of the harvest, and even on the specific time of harvest as well as other growing conditions.
A systematic approach to mitigating the undesirable impact of contaminants present in metathesis feedstocks—particularly though not exclusively natural feedstocks—on the general efficiency and TON of the catalysts used to catalyze the olefin metathesis reaction is desirable.